Process for manufacturing alpha-anthraquinone disulfonate containing low amounts of mercury



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, 3,079,404 PRGCESS FOR MANUFACTURING u-ANTHIRA- QUINONE DESULFONATECBNTAINING LQW AMOUNTS F MERCURY Robert D. Donaldson, Metnchen, andEidred V. Welch, West-field, N1, assignors to General Aniline & FilmCorporation, New York, N.Y., a corporation of Delaware No Drawing. FiledMar. 28, 1960, Ser. N 17,787 7 Claims. (Cl. 260-670) This inventionrelates to an improved process for preparing a-anthraquinone sulfonates,and derivatives thereof particularly 1,8-dihydroxy anthraquinone(Chrysazine), containing low amounts of mercury. In the sulfonation ofanthraquinone, it is known as more fully described in US. Patent2,742,484 of April 17, 1956, that when the sulfonation is effected inthe presence of mercury or mercury compounds as described for example inU.S Patent 742,910 of November 3, 1903, sulfonation in the a-position isfavored, whereas if the sulfonation is effected in the absence ofmercury, then sulfonation in the p-position is favored.

Accordingly, it is common to employ a mercury catalyst in thesulfonation of anthraquinone to produce 1- anthraquinone sulfonic acidand a,a'-anthraquinone disulfonic acids, e.g. the 1,5- or1,8-anthraquinone disulfonic acid or their salts. However, the resultinga-sulfonic acid or salt or a,u'-disulfonic acid or salt still containssubstantial amounts of mercury, which is usually about 1% or higher.This mercury is so combined in the 01- or a,a-anthraquinone sulfonicacid that it is extremely difficult to remove. Accordingly, there hasbeen considerable demand in the art for an inexpensive process by whichthe amount of mercury contained in ocor a,a'-anthraquinone sulfonicacids or their salts, obtained by the sulfonation of anthraquinone inthe presence of mercury, may be reduced to a minimum. The removal of themercury has been particularly important in the case of 1,8-anthraquinonedisulfonic acid, since this is employed as an intermediate for thepreparation of 1,8- dihydroxy anthraquinone, also called Chrysazine,which is employed for medicinal uses. Thus, the National Formulary(1955) has imposed a strict specification requiring that 1,8-dihydroxyanthraquinone (Chrysazine) contain not more than 50 p.p.-m. of mercury.In order to produce Chyrsazine meeting these specifications from1,8-anthraquinone disulfonic acid or its salt, it has been foundnecessary to employ 1,8-anthraquinone disulfonate containing less than0.25% mercury.

We have now found that the mercury content of ozanthraquinonesulfonates, obtained by sulfonation of anthraquinone in the presence ofmercury, and also derivatives of such a-an-thraquinone sulfonates (e.g.1,8- dihydroxy anthraquinone) can be substantially reduced by heatingthe mercury containing m-anthraquinone disulfonate (or derivative) inthe presence of an oxidizing agent. We particularly prefer to use analkali metal bichromate or permanganate, e.g. sodium or potassiumbichromate or sodium or potassium permanganate as the oxidizing agent,however, other oxidizing agents such as nitric acid, hydrogen peroxide,sodium or potassium hypochlorite, chlorine, ammonium-, potassiumorsodium persulfate and the like may be used.

The details of the present invention will be apparent from the followingspecific examples of preferred embodiments thereof.

Example 1 50 g. of paste material of dipotassium 1,8-anthraquinonedisulfonate (containing about 18 g. of 100% dipotassium1,8-anthraquinone disulfonate having a mercury content of about 1% andwhich had been recovered by treating with potassium chloride the acidliquor from 1,5-anthraquinone disulfonic acid manufacture after the1,5-isomer had been separated in a manner similar to the procedure givenin FIAT Report #1016, page 6), was slurried in 50 cc. of water and 10cc. of a 5% solution of potassium permanganate in water was added. Themixture was heated to 95100 C. for 1 hour, then cooled to roomtemperature and the dipotassium 1,8- anthraquinone disulfonate recoveredby filtration, the filter cake being washed with water until free ofpermanganate. The cake was then dried in a vacuum oven at 85-90 C. andon analysis the dry cake was found to contain 0.093% mercury.

Example 2 The foregoing experiment was repeated using, however, in placeof the potassium permanganate 10 cc. of a 5% solution of sodiumbichromate in water. The analysis of the dried dipotassium1,8-anthraquinone disulfonate which was recovered showed that it had amer cury content of 0.077%. The product of both Example 1 and Example 2when employed for the production of Chrysazine gave a material meetingthe specifications of the National Formulary, i.e. Chrysazine containingless than 50 ppm. mercury.

While as indicated inthe above examples, the processof the presentinvention can be applied to dipotassium anthraquinone disulfonate in aconcentrated form, it has been found as illustrated by the followingexample that the process of the present invention can beap'plied to theacid liquors containing the mercury containing 1,8- anthraquinonedisulfona-te having a high mercury content remaining after removal of1,5-anthraquinone disulfonate from the products produced in thedisulfonation of an-thraquinone in the presence of mercury.

Example 3 925 cc. of the acid liquor from 1,5-anthraquinone disulfonicacid manufacture after the 1,5-isomer had been separated in a mannersimilar to the procedure given in FIAT Report #1016, page 6, and whichconsisted largely of mercury containing 1,8-anthraquinone disulfonicacid and a small amount of unsulfonated anthraquinone was diluted withwater to a volume of 2925 cc. The thus diluted liquor was heated to 100C. and 7.5 grams of sodium bichromate added thereto and the mixturestirred for /2 hour at 100 C. The material was then filtered hot on afritted glass filter and a small amount of undissolved, unsulfonatedanthraquinone thus filtered out and discarded. The 1,8-anthraquinonedisulfonic acid was then recovered in the form of its dipotassium saltby cooling the filtrate to C. and adding at 75 C. in /2 hour 45.5 g. ofpotassum chloride. The liquor was tested for complete precipitation ofthe insoluble potassium salt by adding a few crystals of potassumchloride to 5-10 cc. portions of the filter liquor. When the test showedcomplete precipitation in the batch, the batch was cooled to 55 C. andfiltered on a fritted glass filter. The filter cake (dipotassium1,8-anthraquinone disulfonate) was Washed 8 times with 50 cc. portionsof 1.5% potassium chloride solution in water at room temperature. Thefilter cake was sucked as dry as possible, then dried in a vacuum ovenat -90 C. The dry filter cake on analysis had a mercury content of0.23%. In a control run in which the treatment with sodium bichrom atewas omitted, the recovered dipotassium 1,8-anthraquinone disulfonatecontained 1.01% mercury. The dipotassium 1,8-anthraquinone disulfonatecontaining 0.23% mercury was then used as base material for preparingChrysazine in the customary manner by autoolaving with lime followed bydilution, acidification, boil- Example 4 To astainless steel kettleequipped with agitator there was charged 3,330parts by weight of waterand 676 parts by Weight of dry powder Chrysazine (1,8-dihydroxyanthraquinone) which was off standard since analysis showed that itcontained 288 ppm. of mercury. There was also added 1 /2 parts by weightof the nonionic surface active agent obtained by condensing nonylphenolwith about moles of ethylene oxide to aid in wetting out the Chrysazine.The mixture was stirred until the Chrysazine was homogenously dispersedin the water. There was then added 186 parts by weight of 26 B. nitricacid-(35.5% HNOs), Or 65 parts by weight of 100% HNO so as to give 1.85%nitric acid concentration in the kettle. The mixture was heated to 98 C.and held at this temperature while stirring for one hour. The charge inthe kettle was then transferred to a filter and the kettle washed withabout 100 parts by weight of hot water. After filtering, the filter cakewas washed 3 times with 500 parts by weight of hot water until thefiltrate was neutral to Congo red paper. The filter cake was sucked asdry as possible and the filter cake stored in lined drums. There wasrecovered 665 parts by weight (dry basis) of 1,8-dihydroxy anthraquinoneor 98.5% of theory which analysis showed contained 40 ppm. of mercury.

While the present invention has thus far been described in connectionwith the removal of mercury from 1,8-d.i hydroxy anth-raquinone. and1,8-anthraquinone disulfonic acids and its salts, since these materialsare used for pharmaceutical purposes or as an intermediate for thepreparation of a pharmaceutical, 1,8-dihydroxy anthraquinone,(Chrysazine), respectively, which must have a mercury content of lessthanSO p.p.m., it will be understood that the process of the presentinvention can be applied to reduction of the mercury content of othera-su-lfonated anthraquinones which have been produced by sulfonation ofanthraquinone in the presence of a mercury catalyst. Thus by similarprocedures the mercmy content of l-anthraquinone sulfonic acid or itssalts, 1,5-anthraquinone disulfonic acid or its salts, or the mixed 1,5and 1,8-anthraquinone disulfonic acids or salts can be reduced bytreatment with an oxidizing agent in accordance with the presentinvention to reduce the mercury content of each of these isomers so thateither the mixed isomers of low mercury content can be obtained or theindividual isomers, each having a low mercury content, may be separatedfrom this mixture,

We claim:

1. The method of reducing the mercury content of an anthraquinonecompound selected from the group consisting ofl,S-dihydroxyanthraquinone and l,8-anthraquinone disulfonic acid and itssalts which have been produced by the sulfonation of anthraquinone inthe presence of a mercury catalyst which comprises heating in an aqueousmedium said anthraquinone compound together with a small amount of aninorganic oxidizing agent and separating said anthraquinone compoundsubstantially tree of mercury from said aqueous medium.

2. The method as defined in claim 1 wherein the oxidizing agentspecified is potassium permanganate.

3. The method as defined in claim 1 wherein the oxidizing agentspecified is sodium bichromate.

4. The method as defined in claim 1 wherein the oxidizing agentspecified is nitric acid.

5. The method of reducing the mercury content of 1,8-anthraquinonedisulfonic acid dipotassium salt produced by sulfonation ofanthraquinone in the presence of a mercury catalyst which comprisesheating an aqueous slurry of such mercury containing dipotassiuml,8-anthraquinone disulfonate with a small amount of an oxidizing agentselected from the group consisting of nitric acid,

potassium permanganate and sodium bichromate and separating said(ii-potassium 1,8-anthraquinone sulfonate substantially free of mercuryfrom the aqueous phase.

6. The method of reducing the mercury content of (ll-potassium1,8-anthraquinone disulfonate from the acid liquors remaining after theremoval of 1,5-anthraquinone disulfonic acid from the anthraquinonedisulfonic acids produced by sulfonation of anthraquinone in thepresence of a mercury catalyst which comprises heating said acid liquorswith a small amount of an oxidizing agent selected from the groupconsisting of nitric acid, potassium permanganate and sodium bichromate,adding potassium chloride to the thus treated mixture to precipitate thedipotassium 1,8-anthraquinone disulfonate and separating the thusprecipitated dipotassium salt substantially free from mercury from theaqueous phase.

7. The method of reducing the mercury content of 1,8-dihydroxyanthraquinone produced from a 1,8-anthraquinone disultonic acid which inturn was produced by sulfonation of anthraquinone in the presence of amercury catalyst, which comprises heating an aqueous slurry of said1,8-dihydroxy anthraquinone with a small amount of an oxidizing agentselected from the group consisting of nitric acid, potassiumpermanganate and sodium bichromate and separating said 1,8-dihydroxyanthraquinone substantially free of mercury from the aqueous phase.

References Cited in the file of this patent FOREIGN PATENTS 470,503 Gemany Jan. 18, 1929

1. THE METHOD OF REDUCING THE MERCURY CONTENT OF AN ANTHRAQUINONECOMPOUND SELECTED FROM THE GROUP CONSISTING OF1,8-DIHYDROXYANTHERAQUINONE AND 1,8-ANTHRAQUINONE DISULFONIC ACID ANDITS SALTS WHICH HAVE BEEN PRODUCED BY THE SULFONATION OF ANTHRAQUINONEIN THE PRESENCE OF A MERCURY CATALYST WHICH COMPRISES HEATING IN ANAQUEOUS MEDIUM SAID ANTHRAQUINONE COMPOUND TOGETHER WITH A SMALL AMOUNTOF AN INORGANIC OXIDIZING AGENT AND SEPARATING SAID ANTHRAQUINONECOMPOUND SUBSTANTIALLY FREE OF MERCURY FROM SAID AQUEOUS MEDIUM.